A core barrel assembly is used to obtain a cross sectional sample of a particular geological formation. The core barrel assembly utilizes a specialized core bit attached to a number of outer barrels that are interconnected to make up the desired length. The core bit drills downwardly and has a central opening such that the core bit cuts around a column of the formation that is to be the sample. An inner barrel is provided within the outer barrel for receiving the core sample.
During coring, the core bit is designed to drill around a vertical column of the sample such that the inner barrel passes downwardly around the sample. A known problem that can occur during coring is that the core column is not sufficiently stable and collapses downwardly within the inner barrel. The collapsed core column can create additional friction on the inner surface of the inner barrel resulting in jamming of the core.
Observations of the drilling fluid pressure, the torque and the rate of penetration can provide some indication of whether this core collapse has occurred, however it is not possible to rule out the possibility that changes in these values are the result of some other event (such as a change in the formation). The driller is therefore forced to make a decision that could result in continuing drilling when the core is jammed or stopping drilling when the core is not jammed, both situations resulting in an expensive loss of time and effort.
The present invention relates to a system to be used for monitoring the coring operation to provide information on the capture of the core, thereby reducing the likelihood of an undetected core collapse.